feat: question-count tiers, footer in main, pregunta footer

- Pricing: 0,99€/10q · 9,99€/200q · 19,99€/unlimited (all 30 days)
- DB: max_questions + questions_used columns on credits table;
  consumeCreditQuestion() atomically validates, creates question,
  and decrements quota in a single transaction
- Server: updated CREDIT_TIERS, /api/credito/estado returns questionsLeft,
  /api/pregunta/enviar returns updated questionsLeft after each submission
- pregunta.tsx: badge shows live question count; submit disabled when exhausted;
  questionsLeft synced to localStorage after each submission; Cloud Host footer added
- footer: moved from Standings sidebar into <main> (scrolls with game content);
  also added to all pregunta page states

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

db.ts

@@ -105,7 +105,7 @@ export function getPlayerScores(): Record<string, number> {
   return Object.fromEntries(rows.map(r => [r.username, r.score]));
 }
 
-// ── Credits (time-based access) ──────────────────────────────────────────────
+// ── Credits (question-count-based access) ───────────────────────────────────
 
 db.exec(`
   CREATE TABLE IF NOT EXISTS credits (
@@ -120,11 +120,23 @@ db.exec(`
   );
 `);
 
-export function createPendingCredit(username: string, orderId: string, tier: string): string {
+// Migrations for question-tracking columns
+try {
+  db.exec("ALTER TABLE credits ADD COLUMN max_questions INTEGER");
+} catch {
+  // Column already exists — no-op
+}
+try {
+  db.exec("ALTER TABLE credits ADD COLUMN questions_used INTEGER NOT NULL DEFAULT 0");
+} catch {
+  // Column already exists — no-op
+}
+
+export function createPendingCredit(username: string, orderId: string, tier: string, maxQuestions: number | null): string {
   const token = crypto.randomUUID();
   db.prepare(
-    "INSERT INTO credits (username, token, tier, order_id) VALUES ($username, $token, $tier, $orderId)"
-  ).run({ $username: username, $token: token, $tier: tier, $orderId: orderId });
+    "INSERT INTO credits (username, token, tier, order_id, max_questions) VALUES ($username, $token, $tier, $orderId, $maxQuestions)"
+  ).run({ $username: username, $token: token, $tier: tier, $orderId: orderId, $maxQuestions: maxQuestions });
   return token;
 }
 
@@ -146,25 +158,57 @@ export function getCreditByOrder(orderId: string): {
   username: string;
   tier: string;
   expiresAt: number | null;
+  maxQuestions: number | null;
+  questionsUsed: number;
 } | null {
   return db
-    .query("SELECT status, token, username, tier, expires_at as expiresAt FROM credits WHERE order_id = $orderId")
+    .query(
+      "SELECT status, token, username, tier, expires_at as expiresAt, max_questions as maxQuestions, questions_used as questionsUsed FROM credits WHERE order_id = $orderId"
+    )
     .get({ $orderId: orderId }) as {
     status: string;
     token: string;
     username: string;
     tier: string;
     expiresAt: number | null;
+    maxQuestions: number | null;
+    questionsUsed: number;
   } | null;
 }
 
-export function validateCreditToken(token: string): { username: string; expiresAt: number } | null {
+/**
+ * Atomically validates a credit token, creates a paid question, and increments
+ * the usage counter. Returns null if the token is invalid, expired, or exhausted.
+ */
+export function consumeCreditQuestion(
+  token: string,
+  text: string,
+): { username: string; questionsLeft: number | null } | null {
   const row = db
     .query(
-      "SELECT username, expires_at FROM credits WHERE token = $token AND status = 'active'"
+      "SELECT username, expires_at, max_questions, questions_used FROM credits WHERE token = $token AND status = 'active'"
     )
-    .get({ $token: token }) as { username: string; expires_at: number } | null;
+    .get({ $token: token }) as {
+    username: string;
+    expires_at: number;
+    max_questions: number | null;
+    questions_used: number;
+  } | null;
   if (!row) return null;
   if (row.expires_at < Date.now()) return null;
-  return { username: row.username, expiresAt: row.expires_at };
+  if (row.max_questions !== null && row.questions_used >= row.max_questions) return null;
+
+  const orderId = crypto.randomUUID();
+  db.transaction(() => {
+    db.prepare(
+      "INSERT INTO questions (text, order_id, username, status) VALUES ($text, $orderId, $username, 'paid')"
+    ).run({ $text: text, $orderId: orderId, $username: row.username });
+    db.prepare(
+      "UPDATE credits SET questions_used = questions_used + 1 WHERE token = $token"
+    ).run({ $token: token });
+  })();
+
+  const questionsLeft =
+    row.max_questions === null ? null : row.max_questions - row.questions_used - 1;
+  return { username: row.username, questionsLeft };
 }